This process relates to a new apparatus and process for manufacturing continuous sucker rod.
A sucker rod string is the xe2x80x9cdrive shaftxe2x80x9d for powering a down hole pump. At the top end of this drive shaft there is usually an electric motor drive and at the bottom end there is a pump. There are two kinds of pumps used for pumping oil from wells: reciprocating piston pumps and rotary progressive cavity pumps.
Both styles of pump require a similar drive shaft. In order to have sufficient strength this rod string usually requires a tensile strength of 110 ksi , which corresponds to a Rockwell hardness value in the neighborhood of 26 HRc. Rod manufacturers like to use this hardness as a maximum because H2S corrosion rates typically accelerate at hardness values above this value. Heat treating the steel to attain the desired hardness is part of the present day process for producing continuous sucker rod.
Continuous sucker rod strings originally were all rolled to a semi elliptical shape. The reason for using the elliptical shape is to eliminate excessive bending stresses in the rod string when it is compressed into a storage reel that is only 18 feet in diameter. Round rod produces much higher bending stresses when stored in similar reels.
Today round rod is a necessary component to meet the high torsional needs of progressing cavity pumps. In fact the majority of continuous rod produced today is of round cross section and the demand for larger and larger round sections is increasing.
Existing manufacturing of continuous rod begins with the purchase of soft steel coils from steel mills. Coil lengths are typically 1500 feet long, and are wound like garden hose to an inside diameter of 36xe2x80x3 and an outside diameter of 42xe2x80x3. The coil weighs approximately 4500 lbs. The rod diameter is typically xc2xexe2x80x3, xe2x85x9exe2x80x3 or 1xe2x80x3 in diameter. FIG. 1a and FIG. 1b depict an existing transport trailer 10 carrying 18 foot reel 12 that are presently used for transporting finished rod from the manufacturing plant to the customer""s well site. The trailer 10 and reel 12 have dimensions of about 12 foot by 15 foot that define the travelling space required while the trailer is going down the highway. These particular limits are at their maximum. The reel is too small for storing rod without bending it but the road constraints do not allow for anything else.
FIG. 2 denotes a flow diagram for the existing method of manufacture. Once coils reach the manufacturing plant the following process takes place
21. Uncoiling raw material on a mandrel
22. Straightening raw material
23. Flash butt welding uncoiled individual coils together end for end
24. Descaling and cleaning raw material by shot blasting
25. Driving and tensioning raw material
26. Heat treating raw material to the austenizing temperature of the steel used
27. Rolling and stretching material to shape and size
28. Water quenching material
29. Tempering material to a desired steel hardness
30. Quenching material
31. Coating material with a rust inhibitor
32. Loading material on to a transport trailer for shipping to the customers location.
The transport spools are built as large as possible but built to suit the legal dimensional limitations of the motor vehicle regulations in Canada. The actual spool diameter for rod storage is 18 feet. When 1xe2x80x3 diameter sucker rod is put in one of these spools it is stressed to the limit. The rod is actually bent permanently as the surface bending stresses can be as high as 138 ksi.
This invention overcomes the problem of rod bending and coil transportation. Rather than make this sucker rod product and then ship it to the well site on a transport reel, this invention proposes, in one aspect, making the product at the well site using simple equipment. The invention thus provides a portable method for manufacturing continuous sucker rod at any given location that the customer wants the product unloaded and ready for use.
Use of a portable method of manufacturing continuous sucker rod means that the rod can be made at any location that the customer chooses. Therefore the plant facility is forever moving and hence the definitionxe2x80x94xe2x80x9cportablexe2x80x9d. The reason that present plants cannot be portable is twofold: Heat treating equipment requires too much power to be portable and available at any given location. Remote power for flash butt welding is also difficult to find at any given location. Flash butt welding is presently done in the field to repair existing rod strings if they break. This welding process is battery powered and allows for one or two welds without having to recharge.
The process of the present invention does not require heat treating the rod. The raw material is heat treated by the manufacturer and already has the physical properties that are required in the finished product. The reason the existing process includes heat treating after joining lengths is to eliminate heat affected zones produced by welding. The difficulty with this is that all the welds can not be heat treated in such a fashion because the very end connection must be made in the field. Sometimes both rod ends are welded in the field and these welds are left with heat affected zones. Heat affected zones are areas beside the joint that are softer than the parent material once the weld has cooled down. Along with being softer the rod strength in this particular area is decreased in proportion.
Therefore, according to an aspect of the invention there is provided a method of preparing rod for injection into a well, the method comprising the steps of: welding straight lengths of round bar end to end to form welded rod; and coiling the welded rod on a storage reel at a well site. By welding straight lengths of round bar together to make a rod, the process may be conveniently carried out at a well site.
Further aspects of the invention include: transporting straight lets of round bar to the well site, preparing the straight lengths of round bar for welding at the well site, preferably by pencil pointing the ends of the lengths of round bar, with the welding being carried out by MIG welding, grinding and polishing the welded rod, torque testing the welded rod, and coating the welded rod with a rust inhibitor after grinding and polishing. Each length of round bar may be about 40 feet long.
Advantages of the invention include: The plant is totally mobile and the product is made at ever changing well sites. Short bar lengths are welded together instead of long coils being welded together. The welding method is mig welding and not flash butt welding. The welds are not post heat treated and don""t have to be. Transport trailers are not required to transfer finished product as product is made on site.